A driving device is known in which a gear unit comprises a plurality of input shafts, and motors individually coupled to each of the input shafts. An example of this driving device is disclosed in Japanese Patent Application Publication No. 2009-159725. In the description below, Japanese Patent Application Publication No. 2009-159725 is called Patent Document 1. In the driving device of Patent Document 1, the plurality of input shafts is supported by a supporting member. The plurality of input shafts is engaged with driven members, and drives the driven members. The rotors of the motors are respectively attached to the input shafts. More specifically, in the driving device of Patent Document 1, a plurality of crankshafts (input shafts) is supported by a carrier (supporting member), and the plurality of crankshafts is engaged with external gears (driven members). In the driving device of Patent Document 1, a rotor is attached to each of the crankshafts, and stators of all of the motors are attached to the carrier.
In the driving device of Patent Document 1, in all of the motors, the mechanical phase angle of the rotor is aligned relative to the stator. By aligning the mechanical phase angle, all of the motors are controlled by one motor driver. However, it is difficult to affix the stator to the carrier (supporting member) while aligning the phase angle of the rotor. Consequently, in the cited Document 1, in order to align the phase angles of the rotors of all of the motors, the stators are affixed to the carrier while the rotors are in a state of being temporarily fixed to the crankshafts. Then, in-phase current is applied to all of the motors, and the rotors are affixed to the crankshafts in a state where the phase angles of the rotors are aligned relative to the stators.